Allow nil source_uri for Resource

app/models/concerns/triclops/resource/validations.rb

@@ -4,7 +4,9 @@ module Validations
       extend ActiveSupport::Concern
 
       included do
-        validates :identifier, :pcdm_type, :source_uri, presence: true
+        # NOTE: :source_uri is NOT required, since it's okay to create a Resource with no_uri and only a pcdm_type
+        # when derivatives have not yet been created for the resource, but we want to show a pdcm-type-based placeholder.
+        validates :identifier, :pcdm_type, presence: true
         validates :identifier, length: { minimum: 1, maximum: 255 }
         validates :standard_width, :standard_height,
                   :limited_width, :limited_height,

app/models/resource.rb

@@ -58,6 +58,7 @@ def delete_filesystem_cache!
   end
 
   def queue_base_derivative_generation_if_pending
+    return if self.source_uri.nil?
     return unless self.pending?
     CreateBaseDerivativesJob.perform_later(self.identifier)
   end

spec/models/resource_spec.rb

@@ -85,6 +85,12 @@
       expect(CreateBaseDerivativesJob).not_to receive(:perform_later)
       ready_resource.queue_base_derivative_generation_if_pending
     end
+
+    it "does not queue generation for a resource with a nil source_uri, even if it has a ready status" do
+      ready_resource.source_uri = nil
+      expect(CreateBaseDerivativesJob).not_to receive(:perform_later)
+      ready_resource.queue_base_derivative_generation_if_pending
+    end
   end
 
   describe '#switch_to_pending_state_if_core_properties_changed!' do